Olefins are traditionally produced from petroleum feedstock by catalytic or steam cracking processes. These cracking processes, especially steam cracking, produce light olefin(s) such as ethylene and/or propylene from a variety of hydrocarbon feedstock. Ethylene and propylene are important commodity petrochemicals useful in a variety of processes for making plastics and other chemical compounds.
The petrochemical industry has known for some time that oxygenates, especially alcohols, are convertible into light olefin(s). There are numerous technologies available for producing oxygenates including fermentation or reaction of synthesis gas derived from natural gas, petroleum liquids, carbonaceous materials including coal, recycled plastics, municipal waste or any other organic material. Generally, the production of synthesis gas involves a combustion reaction of natural gas, mostly methane, and an oxygen source into hydrogen, carbon monoxide and/or carbon dioxide. Syngas production processes are well known, and include conventional steam reforming, autothermal reforming, or a combination thereof.
Methanol, the preferred alcohol for light olefin production, is typically synthesized from the catalytic reaction of hydrogen, carbon monoxide and/or carbon dioxide in a methanol reactor in the presence of a heterogeneous catalyst. For example, in one synthesis process methanol is produced using a copper/zinc oxide catalyst in a water-cooled tubular methanol reactor. The preferred conversion process converts a feedstock containing methanol in the presence of a molecular sieve catalyst composition to form one or more olefin(s), primarily ethylene and/or propylene.
Molecular sieves are porous solids having pores of different sizes such as zeolites or zeolite-type molecular sieves, carbons and oxides. The most commercially useful molecular sieves for the petroleum and petrochemical industries are known as zeolites, for example aluminosilicate molecular sieves. Zeolites in general have a one-, two- or three-dimensional crystalline pore structure having uniformly sized pores of molecular dimensions that selectively adsorb molecules that can enter the pores, and exclude those molecules that are too large.
There are many different types of molecular sieves well known to convert a feedstock, especially an oxygenate containing feedstock, into one or more olefin(s). For example, U.S. Pat. No. 5,367,100 describes the use of a well known zeolite, ZSM-5, to convert methanol into olefin(s); U.S. Pat. No. 4,062,905 discusses the conversion of methanol and other oxygenates to ethylene and propylene using crystalline aluminosilicate zeolites, for example Zeolite T, ZK5, erionite and chabazite; U.S. Pat. No. 4,079,095 describes the use of ZSM-34 to convert methanol to hydrocarbon products such as ethylene and propylene; and U.S. Pat. No. 4,310,440 describes producing light olefin(s) from an alcohol using a crystalline aluminophosphates, often represented by AlPO4.
One of the most useful molecular sieves for converting methanol to olefin(s) is a silicoaluminophosphate molecular sieves. Silicoaluminophosphate (SAPO) molecular sieves contain a three-dimensional microporous crystalline framework structure of [SiO2], [AlO2] and [PO2] corner sharing tetrahedral units. SAPO synthesis is described in U.S. Pat. No. 4,440,871, which is herein fully incorporated by reference. SAPO is generally synthesized by the hydrothermal crystallization of a reaction mixture of silicon-, aluminum- and phosphorus-sources and at least one templating agent. Synthesis of a SAPO molecular sieve, its formulation into a SAPO catalyst, and its use in converting a hydrocarbon feedstock into olefin(s), particularly where the feedstock is methanol, is shown in U.S. Pat. Nos. 4,499,327, 4,677,242, 4,677,243, 4,873,390, 5,095,163, 5,714,662 and 6,166,282, all of which are herein fully incorporated by reference.
Typically, molecular sieves are formed into molecular sieve catalyst compositions to improve their durability in commercial conversion processes. These molecular sieve catalyst compositions are formed by combining a molecular sieve and a matrix material usually in the presence of a binder. The purpose of the binder is hold the matrix material, often a clay, to the molecular sieve. Binders and matrix materials are typically metal oxides that have a very small surface area such as less than ten square meters per gram (m2/g), more likely less than one m2/g of metal oxide. The use of binders and matrix materials in the formation of molecular sieve catalyst compositions is well known.
U.S. Pat. No. 4,465,889 describes a catalyst composition of a silicalite molecular sieve impregnated with a thorium, zirconium, or a titanium metal oxide for use in converting methanol, dimethyl ether, or a mixture thereof into a hydrocarbon product rich in iso-C4 compounds.
U.S. Pat. No. 6,180,828 discusses the use of a modified molecular sieve to produce methylamines from methanol and ammonia, where for example, a silicoaluminophosphate molecular sieve is combined with one of the modifiers, a zirconium oxide, a titanium oxide, a yttrium oxide, montmorillonite or kaolinite.
U.S. Pat. No. 5,417,949 relates to a process of converting noxious nitrogen oxides in an oxygen containing effluent into nitrogen and water using a molecular sieve and a metal oxide binder, where the preferred binder is titania and the molecular sieve is an aluminosilicate molecular sieve.
Although the use of binders and matrix materials are known for use with molecular sieves to form molecular sieve catalyst compositions, and that these catalyst compositions are useful in a process for converting oxygenates into olefin(s), these binders and matrix materials typically only serve to provide desired physical characteristics to the catalyst composition, and have little to no effect on conversion and selectivity of the molecular sieve. It would therefore be desirable to have an improved molecular sieve catalyst composition having better conversion rates, olefin selectivity, longer lifetimes, and commercially desirable operability and cost advantages.